1. Field of the Invention
The invention relates to a liquid crystal display, and more particularly to a liquid crystal display having left-handed and right-handed cholesteric liquid crystals and a fabrication method thereof.
2. Description of the Related Art
Reflective cholesteric liquid crystal displays have several advantages of high brightness, high contrast, low power consumption, wide viewing angles, and high reflectiveness. The cholesteric liquid crystals used in the reflective cholesteric liquid crystal displays can reflect lights of certain wavelengths. Specifically, a circular polarized light having the same chirality as the cholesteric liquid crystal can be reflected, and another circular polarized light having an opposite chirality will pass through the cholesteric liquid crystal.
In general, the cholesteric liquid crystals are formed by adding a chiral dopant into a nematic liquid crystal host. The chiral dopant can reflect a left-handed light or a right-handed light. When lights permeate through the cholesteric liquid crystals which can reflect a left-handed light, about 50% of the lights would be reflected and another 50% of the lights would pass through the cholesteric liquid crystals. Accordingly, if 100% of light reflection is desired, left-handed and right-handed cholesteric liquid crystals are required to be stacked to enhance reflection.
Europe Patent No. EP1058147 discloses a liquid crystal display, in which a stack of left-handed and right-handed cholesteric liquid crystals is used to increase reflection. The left-handed and the right-handed cholesteric liquid crystals used in this liquid crystal display are polymer-dispersed liquid crystals (PDLC), which are capsulate cholesteric liquid crystals. The cholesteric liquid crystals are packaged into balls for coating in a liquid crystal cell of the liquid crystal display. In addition, U.S. Pat. No. 6,359,673 also discloses a liquid crystal display formed by stacking left-handed and right-handed cholesteric liquid crystals, in which, the left-handed and the right-handed cholesteric liquid crystals are dispersed in the liquid crystal cell in the form of capsules.
However, the required driving voltages of the above cholesteric liquid crystals are relatively high. Additionally, the chemical structures of the chiral dopants in the left-handed and the right-handed cholesteric liquid crystals are not disclosed in the above prior arts. Also, the effects of the chiral dopants on the driving voltages of the left-handed and the right-handed cholesteric liquid crystals are also not disclosed in of the above prior arts.